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Re: [TenTec] RFI question for Orion and other TT rigs

To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Subject: Re: [TenTec] RFI question for Orion and other TT rigs
From: "Stuart Rohre" <rohre@arlut.utexas.edu>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Tue, 28 Jun 2005 14:27:43 -0500
List-post: <mailto:tentec@contesting.com>
Absolutely RIGHT Bob,

That hams need to understand the difference in why you use a ground rod and
the other grounds in radio.  (Rod-Electrical safety only, static discharge
ground for arrestors).

And the Radials- base of short quarter wave or less verticals, or
counterpoise, (above ground radial).  Is an RF ground.

The counterpoise in shack- quarter wave insulated wires for each band, to
help a shack that is raised physically a quarter wave or more above a
physical RF ground re-establish a low RF impedance on the rig chassis.
-Is an RF high potential control conductor.

And no radials needed:  (antenna is complete RF wise)- (half wave verticals,
horizontal balanced antennas with center feed, beams, Moxons, etc.)

Note off center antennas impose an imbalance that may need counterpoise.
OCF's, Carolina Windom, and the original Windom are thus unbalanced by
virtue of unequal flat top conductor lengths.

And physical ground itself.  Is NEVER a good RF ground alone.  Only in
extraordinary cases will driving a ground rod help with an RF problem.  More
than likely, the length of conductor you added, to reach the rod, is acting
as a counterpoise wire, moving the high RF point off the rig chassis and out
the shack to the end of the conductor near the rod.

Many places like New England, Southwest, Tropics, Deserts, have terrible RF
character in their local earth ground, and cannot be relied on for RF low
impedance---no matter how many ground rods you might sink.

Hams need to realize that to be a good RF ground, the earth would have to be
a metallic low impedance conductor of RF.  "Dirt don't do it".

Those who are so concerned about running around driving ground rods to solve
RF problems, should answer the question:

-Where do you drive the ground rod for a spacecraft in orbit?  Yet their
radios work from HF to microwaves just fine.

The ground rod is seldom a significant portion of a wavelength at HF
frequencies, thus will be a poor fraction of a wavelength counterpoise.

Driving ground rods vertically is often impossible to adequate depth for
lightning protection.   Digging a trench and laying out a circumferential
ground wire around the house/ station will do as well.  200 feet of no. 10
bare has been calculated by Austin Energy here,  to equal the best 9 foot
ground rods.  Eighteen inches deep is doable at most sites, and is
completely adequate depth.  For lightning protection you want current
spreading, so conductor area in contact with soil becomes paramount.

-Stuart Rohre

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